1. Field
Embodiments of the present invention relate to a semiconductor device and a semiconductor device manufacturing method.
2. Description of Related Art
A discrete power semiconductor device with a high breakdown voltage plays an important role in a power conversion equipment. For example, an insulated gate bipolar transistor (IGBT), metal oxide semiconductor field effect transistor (MOSFET), and the like, are among commonly known discrete power semiconductor devices. In particular, as the IGBT has the characteristic of low on-state voltage due to the effect of conductivity modulation, it is usually applied when power conversion at a high voltage is needed.
FIG. 26 is a sectional view showing a heretofore known IGBT. In the IGBT shown in FIG. 26, an n+ buffer region 108 and an n− drift region 102 are stacked on a p+ substrate 101 that forms a p+ collector region. A p-base region 103 and an n+ emitter region 104 are selectively provided in a surface layer of the n− drift region 102. A gate electrode 106 is provided across a gate insulating film 105 on the p-base region 103 sandwiched by the n+ emitter region 104 and drift region 102 on the surface of the n− drift region 102. An emitter electrode 107 short circuits the p-base region 103 and n+ emitter region 104.
A description will be given of an action of the IGBT. When a voltage of a threshold value or higher is applied to the gate electrode 106, a channel allowing electrons to pass through is formed in the p-base region 103 in the vicinity of the gate insulating film 105, a voltage drop occurs between the n− drift region 102 and n+ emitter region 104, and a current flows (conducting state). This voltage drop at a rated current is an on-state voltage Von. Electrons are implanted into the n− drift region 102 from the n+ emitter region 104 side, and holes are implanted from the p+ substrate 101 side. Because of this, the number of electrons and holes in the n− drift region 102 is far greater than in the n+ buffer region 108 in contact with the n− drift region 102.
Meanwhile, when the voltage applied to the gate electrode 106 is reduced to the threshold value or lower from the conducting state, the electrons and holes in the n− drift region 102 move from the n− drift region 102 to another region, an electron barrier is formed between the n− drift region 102 and n+ emitter region 104, and the current is cut off. An energy loss Eoff occurs in the process of transiting from the conducting state to the current cutoff state. In this way, the on-state voltage Von and energy loss Eoff are in a trade-off relationship.
In the IGBT shown in FIG. 26, in order to improve this kind of IGBT performance trade-off, a region (hereafter referred to as a lifetime control region) 110 that controls minority carrier lifetime is provided in a p+ collector region 109 provided in a surface layer of the p+ substrate 101 on the n+ buffer region 108 side. The lifetime control region 110 is provided in the vicinity of the interface between the n+ buffer region 108 and p+ collector region 109, distanced from the interface.
The following method is proposed as a method of fabricating an IGBT with improved trade-off. The lifetime control region 110 is formed in a surface layer of one main surface of the p+ substrate 101 using ion implantation and annealing. The ion implantation is carried out using an n-type impurity such as, for example, helium (He), with an acceleration energy of 340 keV and a dose of 2.0×1015 cm−2 to 4.0×1015 cm−2. The annealing is carried out, for example, at 700° C. for 60 minutes, with the inside of an annealing furnace in a vacuum state. Next, the p+ collector region 109, n+ buffer region 108, and n− drift region 102 are stacked, in that order, on the surface of the lifetime control region 110, using epitaxial growth. Next, an IGBT surface structure is formed on the front surface (hereafter referred to as the front surface of the n− drift region 102) side of an n− substrate that is to form the n− drift region 102, thereby completing the IGBT shown in FIG. 26 (for example, refer to Non-patent Document 1).
Also, as another method, the following method is proposed. FIG. 27 is a sectional view showing another example of a heretofore known IGBT. An impurity region that is to form a lifetime control region 220 is formed in a surface layer of one main surface of a p+ substrate 201, using ion implantation. The impurity used in the ion implantation is, for example, tungsten (W) or tantalum (Ta). Next, an n− drift region 202 is deposited on the surface of the lifetime control region 220, using epitaxial growth. At this time, the impurity region formed in the surface layer of the p+ substrate 201 diffuses to the n− drift region 202 side. Because of this, the lifetime control region 220 is formed in the vicinity of the interface between the p+ substrate 201 and n− drift region 202. Next, a trench gate structure portion formed of a p− base region 203, an n+ emitter region 204, a p+ contact region 208, a gate insulating film 205, a gate electrode 206, and an emitter electrode 207 is formed in a surface layer of the n− drift region 202, thereby completing the IGBT shown in FIG. 27 (for example, refer to Patent Document 1).
FIG. 28 is a sectional view showing another example of a heretofore known IGBT. An n-buffer region 209 is formed in a surface layer of one main surface of the p+ substrate 201, and an impurity region that is to form the lifetime control region 220 is formed in a surface layer of the n-buffer region 209, using ion implantation. Next, the n− drift region 202 is formed on the surface of the n-buffer region 209. In this case, by the impurity ion implanted into the surface layer of the n-buffer region 209 being diffused to the n− drift region 202, the lifetime control region 220 is formed in the vicinity of the interface between the n− buffer region 209 and n− drift region 202. The method of forming regions other than these is the same as for the IGBT shown in FIG. 27.
FIG. 29 is a sectional view showing another example of a heretofore known IGBT. In the IGBT shown in FIG. 29, a non-activated region (lifetime control region) 210 is provided between the n− drift region 202 and n-buffer region 209. The lifetime control region 210 is formed as follows. The n-buffer region 209 and a p+ collector region 211 are formed sequentially in a surface layer of the rear surface (hereafter referred to as the rear surface of the n− drift region 202) of a substrate that is to form the n− drift region 202, using ion implantation and annealing. Next, an ion implantation for forming the lifetime control region 210 is carried out from the p+ collector region 211 side into the n− drift region 202. The ion implantation conditions are, for example, using an n-type impurity such as phosphorus (P), an acceleration energy of 500 keV, and a dose of 1.0×1014 cm−2. Next, a collector electrode 212 in contact with the p+ collector region 211 is formed. The lifetime control region 210 is formed by thermal diffusion due to heat treatment for forming the collector electrode 212 (for example, refer to Patent Document 2).
FIGS. 30 to 33 are sectional views sequentially showing a method of manufacturing another example of a heretofore known IGBT. As shown in FIG. 30, firstly, the n+ buffer region 108 is formed in the surface layer of one main surface of an n− substrate that is to form the n− drift region 102, using ion implantation and annealing. An n-type impurity such as, for example, phosphorus is used in the ion implantation. Next, as shown in FIG. 31, an ion implantation for forming the lifetime control region 120 is carried out into the surface of the n+ buffer region 108. The ion implantation is carried out using, for example, argon (Ar) or the like, with an acceleration energy of 150 keV, and a dose of 3.0×1015 cm−2. Next, as shown in FIG. 32, the face of the n− substrate on the side on which the n+ buffer region 108 is formed, and the p+ substrate 101 prepared in advance, are bonded together. Next, the n− substrate is thinned by grinding from the face of the n− substrate on the side opposite to the face on the side on which the n+ buffer region 108 is formed. Next, as shown in FIG. 33, a planar gate structure portion is formed in the same way as for the IGBT shown in FIG. 26. The lifetime control region 120 is formed by the heat treatment in each step or process in the vicinity of the interface between the n− drift region 102 and n+ buffer region 108. That is, the lifetime control region 120 is provided away from a junction 113 at which the n− substrate and p+ substrate 101 are bonded together (for example, refer to Patent Document 3 and Non-patent Document 2).
FIG. 34 is a sectional view showing another example of a heretofore known IGBT. In the IGBT shown in FIG. 34, an n-type impurity such as arsenic (As) is implanted into the rear surface of an n− substrate that is to form the n− drift region 202. Next, an annealing process (laser annealing process) is carried out by irradiating the rear surface of the n− substrate in a striped form with a laser, leaving gaps at equal intervals. By so doing, an n-buffer region 240 and lifetime control region 250 activated in a striped form are formed simultaneously. Next, the p+ collector region 211 is formed by implanting a p-type impurity such as boron (B) into the surfaces of the n-buffer region 240 and lifetime control region 250, and carrying out a laser annealing process. Next, the collector electrode 212 in contact with the p+ collector region 211 is formed, thereby completing the IGBT shown in FIG. 34. The method of forming regions other than these is the same as for the IGBT shown in FIG. 27 (for example, refer to Patent Document 4).
Also, a reverse blocking IGBT (RB-IGBT), in which a termination structure is provided to realize a high breakdown voltage (hereafter referred to as a reverse breakdown voltage) when reverse bias is applied to a p-n junction formed of a collector region and drift region of a heretofore known IGBT, is commonly known. In RB-IGBT, in the same way as in the heretofore described IGBTs, the on-state voltage and energy loss are also in a trade-off relationship.
FIG. 35 is a sectional view showing a heretofore known reverse blocking IGBT. In the reverse blocking IGBT shown in FIG. 35, a p-collector region 111 is provided in a surface layer of the rear surface of an n− substrate that is to form the n− drift region 102. A collector electrode 112 is in contact with the p-collector region 111. A p-type through-silicon isolation region 130, which penetrates through the n− drift region 102 from the front surface of the n− drift region 102, reaching the p-collector region 111, is provided in an outer peripheral end portion of the n− drift region 102. A field plate 131 is in contact with the isolation region 130. A floating p-region 141 and a field plate 142 in contact with the p-region 141 being provided on the front surface side of the n− drift region 102, a termination structure 140 formed of the p-region 141 and field plate 142 is formed. The isolation region 130 and termination structure 140 surround an active region 100 through which a drift current flows. A p+ contact region 122 in contact with the n+ emitter region 104 is provided in a surface layer of the p-base region 103 in the active region 100. An n-region 121, which covers the p-base region 103 to a region below the p-base region 103, is provided in the surface layer of the n− drift region 102. Configurations of the active region 100 other than this are the same as in the IGBT shown in FIG. 26.
As shown in FIG. 35, it is necessary to form the isolation region 130 in the outer peripheral end portion of the n− drift region 102 in order to fabricate the reverse blocking IGBT. The following method is proposed as a method of forming the isolation region 130. A p-type impurity such as boron (B) is selectively implanted into the front surface of the n− drift region 102, forming a p-impurity region, and diffused for a long time at a high temperature. This p-impurity region is the isolation region 130. Next, the IGBT surface structure is formed on the front surface side of the n− substrate. Next, the rear surface of the n− substrate is ground until the isolation region 130 is exposed. By so doing, the isolation region 130 is formed reaching the p-collector region 111 from the front surface of the n− drift region 102.
Also, as another method, the following method is proposed. FIG. 36 is a sectional view showing the manufacturing process of a heretofore known reverse blocking IGBT. As shown in FIG. 36, a p-type impurity is implanted into the whole of the rear surface of an n− substrate that is to form the n− drift region 102, and diffused. By so doing, the p-collector region 111 is formed over the whole of the rear surface of the n− drift region 102. Next, a p-type impurity is selectively implanted into the front surface of the n− substrate that is to form the n− drift region 102, thereby forming a p-type impurity region. Next, the p-type impurity region is diffused until it reaches the p-collector region 111. The isolation region 130 is formed reaching the p-collector region 111 from the front surface of the n− drift region 102 (for example, refer to Patent Document 5 (FIG. 2)).
FIG. 37 is a sectional view showing a heretofore known reverse blocking IGBT. In the reverse blocking IGBT shown in FIG. 37, a p-type isolation region 150 is provided along the side walls of a trench reaching the p-collector region 111 from the front surface of the n− drift region 102, connecting with the p-collector region 111. The trench surrounds the active region 100 and termination structure 140 of the n− drift region 102. A filling material 151 is embedded inside the trench. Configurations other than this are the same as in the reverse blocking IGBT shown in FIG. 35.
As a method of forming this kind of trench structure isolation region, there is proposed a method whereby a process of forming a second conductivity type first impurity region on the second main surface side of a first conductivity type semiconductor substrate having a first main surface and a second main surface opposing the first main surface, a process of forming a trench in a peripheral region of the semiconductor substrate so as to reach the first impurity region from the first main surface, using anisotropic etching, and a process of forming a second impurity region by introducing a second conductivity type impurity into the semiconductor substrate from a trench side wall using ion implantation, are sequentially carried out (for example, refer to Patent Document 6).
FIG. 38 is a sectional view showing another example of a heretofore known reverse blocking IGBT. In the reverse blocking IGBT shown in FIG. 38, a p+-type isolation region 160 and the reverse blocking IGBT surface structure are formed on the (100) plane (front surface) side of the n− drift region 102. The IGBT surface structure is the same as in the reverse blocking IGBT shown in FIG. 35. Next, the n− drift region 102 is thinned to a predetermined thickness from the rear surface side of the n− drift region 102. Next, a depressed portion 161 is formed, penetrating the n− drift region 102 from the rear surface side of the n− drift region 102, and reaching the front surface. Herein, the side walls of the depressed portion 161 form an angle of, for example, 54.7° with the rear surface of the n− drift region 102. Next, using ion implantation and annealing, the p-collector region 111 is formed in the rear surface of the n− drift region 102, and a p+ region 162 is formed in the side walls of the depressed portion 161. Because of this, the isolation region 160 is formed connected to the p-collector region 111 across the p+ region 162.
The following kind of method is proposed as a method of forming an isolation region in a reverse blocking IGBT wherein the outer peripheral end portion is thinner than the active region side in this way. The surface of a thin semiconductor wafer on which is formed a surface structure configuring a semiconductor chip is attached to a support substrate with two-sided adhesive tape. Next, a trench that is to form a scribe line is formed from the rear surface of the thin semiconductor wafer using wet anisotropic etching, exposing the crystal surface. Next, an isolation layer that maintains reverse breakdown voltage in the side surfaces of the trench in which the crystal surface is exposed is formed simultaneously with a p-collector region, which is a rear surface diffusion layer, using ion implantation and low temperature annealing or laser annealing (for example, refer to Patent Document 7).